The following references to and descriptions of prior proposals or products are not intended to be, and are not to be construed as, statements or admissions of common general knowledge in the art. In particular, the following prior art discussion does not relate to what is commonly or well known by the person skilled in the art, but assists in the understanding of the inventive step of the present invention of which the identification of pertinent prior art proposals is but one part.
A complete lighting unit or luminaire may include a lamp bulb or tube combined with a bayonet or screw-in base to form a lamp unit, a lamp holder to receive the lamp base to electrically connect the lamp to the holder, a protective transparent or translucent cover encasing the lamp and holder and connectors to a power source. Although the prior art and the invention will generally be described with reference to street lighting, it will be appreciated that the invention has applicability in relation to other applications in the fields of heavy transport, rail, mining and industry. Street lighting typically includes a lamp comprising a high or low pressure sodium lamp tube and a screw-in base. The screw-in base is made according to standards used, whereas in the US an E39 39 mm screw-in base is used according to local standards. In Australia, the European standards are adhered to, although given the closeness in dimensions, the US E39 39 mm screw-in base is effectively interchangeable in most Australian street lamp fittings.
In street lighting, in standard arrangements the lamp unit is inserted into a porcelain lamp holder that houses a metal threaded (female) socket providing the axial and cylindrical wall electrical contacts. The axial contact is typically spring loaded to improve the reliability of the axial contact and to provide engagement of the base under tension in the holder socket. However, in the street lighting environment and other lamp applications where low frequency vibrations are part of the operating environment, there is a tendency for the screw-in base to unthread by the combined action of the low frequency vibrations and the spring loaded centre contact. The loosening and unthreading of the screw-in base by axial displacement away from the spring loaded centre contact ultimately may open up a gap between the respective axial terminals leading to a condition in which arcing and discharge can occur. Arcing may lead to failure of the luminaire as a result of damage to the lamp holder, holder mounting and metal socket, so that simple replacement of the lamp unit will not repair the luminaire. Instead, considerable man hours, optionally use of expensive equipment such as cherry pickers, repair of damage to the porcelain lamp holder mounting and replacement of both the lamp holder and the lamp unit are normally required.
High quality, long life high pressure sodium lamps are available and are preferred unit components for many applications due to the potential for long-life and the reduction in maintenance and repair costs. However, the early occurrence of the loosening of the screw-in base can and does lead to, arcing and damage to the luminaire. Such damage is often caused by welding of the metal contacts of the lamp and lamp holder together due to the heat from discharge caused by the arcing. This significantly reduces the advantages offered by the use of long-life lamp technology.
It is noted that it becomes difficult to remove lamps that have failed as a result of arcing as often the heat welds the metal contacts of the lamp and lamp holder together. Moreover, the porcelain base of the lamp holders may be irretrievably damaged and difficult to remove. What should be a routine matter of replacement of a lamp becomes a major repair job to replace the lamp holder as well as repairing any damage to the holder mount.
Accordingly, a significant issue associated with optimising the life of industrial and transport lighting is the need to ameliorate the effects of low frequency vibrations on the screw engagement of the base in the socket.
Such low frequency vibrations are wholly or partially absorbed by the dampening device. The device, when in the form of the annular ring may be mounted as a short sleeve on the shaft of the screw-in base. Preferably, the annular ring is pushed or rotated around the thread up the screw-in base until it abuts the base of the tube, so that the annular ring forms a seal or gasket at the upper end of the socket and the screw-in base. The annular ring may therefore perform as a seal or gasket and thereby protect the socket against ingress of dust, grime and moisture, further preserving the socket and base against corrosion and other deterioration.
Efforts have been made to solve the problem of the loosening of the screw-in base by providing multiple wire spring formed in the internal wall of the female threaded socket in an attempt to hold the screw-in base in place against the spring loaded centre contact. However, whilst such arrangements may delay the damage occasioned by the unthreading of the screw-in base, unthreading still inevitably occurs well before the expected expiration of the life of the lamp tube.
An object of the present invention is to ameliorate the aforementioned disadvantages of the prior art to at least provide a useful alternative thereto.